1. Field of the Invention
This invention relates to a process for producing rubbery polymers and random copolymers having branched structures from which improved physical properties are brought about.
2. Description of the Prior Art
In recent years, the rubbery polymers obtained by using an alkyllithium catalyst are gaining more and more important position in the field of vulcanized rubber since they normally have quite excellent performances such as the abrasion resistance, low temperature characteristics, flex-cracking resistance, dynamic properties, etc.
However, these rubbery polymers obtained by using the organolithium catalyst are known heretofore to have practically perfect linear structures, lacking completely the branched structures in their molecules, as described in Industrial and Engineering Chemistry, Johnson, B. L., 40, 351 (1948), Journal of Polymer Science, Part C, No. 1, p. 311 (1963) and Part A, No. 2, p. 797 (1964). Thus, they have drawbacks in that their flow properties at room temperature or so-called "cold flow, " are extremely high, and that the tensile strength and tear resistance of the unvulcanized rubber are poor due to the less entanglement among the molecules.
Because of these drawbacks as mentioned above, there have been often involved some difficulties in the processing operations of these rubbery polymers prior to the vulcanization thereof and, as a result, the utility of these rubbery polymers known heretofore has been greatly restricted in spite of the excellent performances belonging to them.
Heretofore, in order to prevent the flow properties at room temperature, there have been proposed a number of methods which may be generally classified into the following three groups:
1. Methods of giving chemical cross-linking among the rubber molecules by the incorporation of a cross-linking agent having polyfunctional group, as disclosed in Dutch Pat. No. 6,602,265. PA1 2 Methods of giving cross-linking among the rubber molecules by using a radical generating reagent as described in the specification of British Pat. No. 1,018,364. PA1 3. Methods of preventing the cold flow by blending of a different type of polymer as disclosed in U.S. Pat. Nos. 3,244,773 and 3,240,841.
However, the methods for preventing the cold flow proposed heretofore based on these conceptions as generally classified into the above-mentioned three groups are inevitably accompanied by the deterioration in the performances of the rubbery polymers and, sometimes, an extreme degradation in the processability.